HEATER BLOWS OUT COOL AIR.

1999 Hyundai Tiburon

Heater problem
1999 Hyundai Tiburon 4 cyl Front Wheel Drive Automatic

My heater was working perfectly last winter. Now, the heater is blowing out cool air. I checked the fuses and they are all good. I took it to a mechanic and he said somthing about a heater control or somthing like that. Pleas help winter is coming ! Thank you.